Substitution
by staringatstars07
Summary: Gaster has a new test subject. This time, it's a volunteer.


Gaster's new test subject seemed to interact with their surroundings solely on a level of extremes. It's not really their fault, though. Ever since they'd appeared out of nowhere with their exceptionally strange request - "Take the power out of me. I don't want it." - the Royal Scientist's been obsessed with the idea of extracting their DETERMINATION. He's convinced that they're the reason for the fluctuations in time, the shifting and stopping and starting of the timelines. So, uh, he's not exactly giving them the breathing room to act any other way.

"Imagine it, Sans." Gaster had gushed to him excitedly during their lunch break. Well, Sans' lunch break. Good ol' Gaster believed eating to be an activity only indulged by the weak. "Imagine all the good we could do for monster kind, the leaps and bounds forward this will take our research."

And he did imagine it – a world where he and his brother were safe, a world where they could be free. He loved science, it was one of the few things about himself he could take a certain measure of pride in, but beneath his love of formulas and equations, he'd always harbored a secret yearning to see the stars.

Unmoving. Ever changing. Infinite.

But that… still didn't make what they were doing right.

Gaster had the subject blindfolded – it had to be wrapped around almost twice over because their head was so much smaller than the average monster's – had their arms and legs strapped to a vertical gurney so they couldn't squirm. They hadn't seen anything other than the insides of their eyelids for days, hadn't moved or stretched their legs. And if the experiments didn't end with them screaming until their voice rasped against the inside of their mouth and throat like sandpaper, it ended with them dead.

That was their power, the thing they wanted gone so badly they'd subject themselves to torture to get rid of it.

SAVE.

RESET.

As far as he could tell, the anomaly didn't save their life so much as it shifted the timeline to one where they hadn't died yet, making it so that the only way for time to move forward was to cancel the experiment.

According to the records, time had jumped backwards – sideways? – dozens of times already, and the human hadn't broken once.

Gaster postulated that their resilience was a side effect of their DETERMINATION, as though it were the symptom of some sort of illness.

But Sans was good at reading faces, and though the kid was no coward, it wasn't bravery he saw when he studied the line of their mouth, the never quite dried tear tracks glistening on their cheeks.

It was guilt. Pure and simple.

And way more self-hatred than he was used to seeing outside of a mirror. It didn't matter what they'd done or what they wanted to atone for, that expression… it didn't belong on a child.

Sans watched through the two-way glass as a needle the length of the kid's arm punctured an arterial vein in the human's neck. Instead of crying out the way any other child would have, they clamped down on their bottom lip, biting down until blood dribbled down their chin. It didn't – couldn't keep them from cringing away as the source of the sudden burning sensation in their neck plunged deeper.

"Hm," Gaster mused, "perhaps more restraints are in order."

There was a splintering sound. Sans glanced down at the skeletal fingers he'd absently placed on the window to see he'd applied enough pressure to send cracks spidering through the glass.

Whoops.

Beside him, Gaster gave his signature creepy smile, the one that frightened most of the interns away, oblivious to how close his window had come to crashing down in front of him. "hey, dr. gaster," with a slowness that perfectly conveyed his reluctance to look away from his favorite test subject, the scientist turned to face him, "why don't you let me take care of the kid tonight? how many days has it been since you slept?"

"I am a skeleton, Sans," he replied with an irritated snap. "You of all people should know that I do not require rest."

"that's true," Sans shrugged, "but it helps. go home. the kid's not going anywhere without help."

At this point, the lab was more of a home to Gaster than the sad, poorly kept dwelling he sometimes visited for supplies, but he conceded the point, regardless. Sleep, though not vital, was certainly not ill-advised.

Once he'd departed, Sans picked up the lunch box Papyrus had packed for him – a PB & spaghetti sandwich? Nice. – unlocked the room where they kept the human, and slipped inside.

The human didn't hear him at first. Too busy dealing with the lingering pain and the monsters inside their own head, he guessed as they choked back a fresh wave of sobs.

"Sans," he started at the sound of his name. It was quiet as a whisper, a tired rasp in a ruined throat. "I'm so sorry."

A strong desire to comfort the kid crawled up his spinal column. He plopped himself down on the ground beside their feet, carefully unpacking his lunch as he chewed on whether or not seriously getting invested in the kid was a good idea. Then again, it was already too late for him not to care.

"what's your name?" The sandwich tasted like stringy ice in his mouth. Guess Pap left it out to cool for too long. It was always hard to judge temperature when you didn't have any skin. "you have one, right?"

Their head swiveled to face him, jaw dropped slightly in shock. If he didn't know better, he'd say the kid recognized his voice. They didn't say anything for a while, then, "Doesn't everyone?"

Ah, trying to deflect the Deflection Master, were they? Well, it wouldn't hurt to bite.

"some monsters, especially ones created in a lab, have to choose their own names." An easy shrug. "can't go around calling ourselves Subject 01 and Subject 02, right? doesn't exactly roll off the tongue." He set aside half of his sandwich, then popped open a Sea Tea without taking a sip.

"F-frisk." They fumbled with the sounds, stuttering over the word as though it were a precious, irreplaceable treasure made of the clearest crystal and saying it aloud might break it or tear it straight from existence.

Sans hummed quietly, mulling over this new piece of information. "i've heard that name before, haven't i?"

There was a moment's hesitation, a flash of guilt. "…Not in this timeline."

Rubbing the back of his skull, Sans said, "look, i don't know what you've done, kid, but i'm having some trouble stomaching what we're doing to you here." He paused, then continued, "And that's saying something because i don't have a stomach." The kid snorted, honestly amused for the first time since he'd known them. Sans chuckled. "you're an easy audience, frisk." He fished a key out of his lab coat's front pockets. "sorry for leaving you hanging for so long."

The straps came loose as Sans quickly went about unlocking each and every one of them.

As he worked, Frisk frantically shook their head. "What are you doing? You can't let me go. I can still RESET." The last strap came undone. Sans caught them before they collapsed. They sagged in his arms, exhausted, drained. Tentatively, they looked up to find his face in the dark. With quick, sure fingers, Sans untied the blindfold to find swollen, bloodshot eyes, skin made red and raw from the constant rub of the fabric as they thrashed. "Why are you being so nice to me?"

No wonder he'd grown a soft spot for the kid. They were small, hurt, and sadder than anyone so young had any right to be. "look, good people can do bad things for the right reasons, and for the wrong reasons, too. if you're really sorry, then find a way to fix things."

An unexpectedly suspicious glance met his words. "The Sans I know would never say that. He hates RESETs."

"that's your problem right there, kid. you don't need time travel to say you're sorry." Jabbing a thumb towards the exit, he said, "it's time to stop hiding, buddy. if I know me, and i think i do, then your sans is probably worried about you." The kid still looked doubtful, but that was okay. Then they looked down to find their arms were filled with half a sandwich and a Sea Tea.

Sans could practically see the question marks floating over their head. Unfortunately, it didn't distract them as much as he'd hoped. "If I go… Gaster won't hurt you, will he?"

"ah, come on, kid. i'm already a skeleton. what more can he do?" They shook their head, brow furrowed with worry. In an attempt to erase some of that awful crease between their eyes, he plunged his fingers through their hair and ruffled it. It was dirty and knotted and it needed a wash, but the act seemed to finally lift their spirits, even if only a little. It was a start. "that bad, huh? well, i can handle myself, and who knows what trouble gaster would get himself into if i'm not around? so it's okay. go home. go find your friends. i'm sure you've got better things to do than hang out here with us nerds."

By the time Gaster returned to check on the subject, all that was left of his grand experiment was an empty gurney and his lab assistant, who appeared to have fallen asleep waiting for him. Sans woke up with a snort. "heya."

Possibilities ran through his mind, along with a long list of all the lost opportunities. Losing the test subject was a setback his research would never recover from. And Sans hardly looked too broken up about it. "How did they escape?"

"who knows? i had my eyes peeled the whole time. guess they got lucky."

While massaging the bridge of his nasal cavity, Gaster replied through a clenched jaw, "You don't have eyes."

"oh. really?" Sans stuck a hand into one of his eye sockets, groped around experimentally, then pulled it back out with an audible popping noise. "would you look at that? no wonder they got past me."

Gaster, who'd gone forebodingly silent during Sans' little performance, took a deep breath, the air rattling his bones as it rushed through his rib cage. "It would seem… that we are in need of a new test subject." The words weren't unexpected, but they still cut through the sterile atmosphere with the force of a bullet, and the steely, unforgiving nature of a blade. For once, Sans didn't bother replying. Instead, he waited, arms crossed over his chest, for what came next, the permanent smile carved on his face grim and mirthless.

Without warning, the straps from the gurney lifted on their own accord, shooting across the room to wrap themselves around thin skeletal legs and arms. They pinned Sans against the cold metal as one threaded itself through his jaw. In hindsight, Sans thought as the good doctor approached with his hands clasped and his posture hunched, it would have been better for everyone if he'd just left with the kid. "Thank you, Sans. For volunteering your services to this project."


End file.
